The present invention relates generally to a radio frequency (RF) communication transceiver, and more particularly relates to a transceiver, such as a Frequency Shift Keying (FSK) transceiver, which employs Time Division Duplexing (TDD) to support full duplex wireless communications.
Currently, high frequency radio frequency (RF) communications are becoming more and more prevalent in the world today. Products touting wireless RF communication links are becoming increasingly popular among consumers. Today, there are an increasing number of new products, including redesigned existing ones, being designed incorporating wireless RF links.
Most of the RF communication circuits found in wireless products employ some form of oscillator and synthesizer circuitry in their transceivers. Due to the explosive consumer demand for products sporting wireless communication links, there is a need for low cost transceivers that are suitable for mass manufacture.
In addition, the sharing of certain elements between several functions in radio communications transceiver provides a reduction in cost and size, both of which are desirable.
Radio communication TDD transceivers that share at least one element are known in the art. U.S. Pat. No. 5,689,819, issued to Nishimura et al., discloses a transceiver wherein a quartz crystal oscillator is used as a common reference signal for the local oscillators in the receive section of the transceiver and for the generation of the carrier signal for use in the transmit portion of the transceiver. The output signal of the quartz crystal oscillator is input to three separate VCOs used to generate the LO signal for the transmitter, the first LO signal for the first IF stage and the second LO signal for the second IF state. A disadvantage of this transceiver is that although the quartz crystal oscillator is shared, an independent VCO is used to generate each LO signal. the quartz crystal oscillator is shared, an independent VCO is used for the generation of each LO signal.
U.S Pat. No. 5,123,008, issued to Beesley, discloses a time division duplex transceiver wherein the first receiver local oscillator in a dual conversion superheterodyne receiver doubles as the frequency source for the transmitter. A selected harmonic of a separately generated second receiver local oscillator signal is used to derive the LO for the second receiver. Here too, a disadvantage is that multiple oscillators are required to generate the LOs used in the transceiver.
The present invention provides the ability to create a complete communications transceiver utilizing a single oscillator for both transmitting and receiving without comprising performance over other designs that incorporate more than one oscillator. The radio transceiver comprises a single synthesized oscillator having high harmonic content. The transceiver also comprises a power amplifier on the transmit path. On the receive path, the transceiver comprises a low noise amplifier (LNA), a plurality of frequency conversion mixers and a demodulator.
A key feature of the present invention includes the implementation of a single voltage controlled oscillator (VCO) running at a closed loop controlled fundamental frequency whereby the harmonic products generated by the VCO are used for both transmission and reception. The use of a single VCO and associated supporting circuitry for both transmit and receive portions of the circuit serves Lo reduce the cost of a transceiver.
It is important to note that the principle of utilizing the fundamental and harmonic frequencies of a single oscillator can be applied to a transceiver regardless of the type of modulation scheme employed, e.g., FSK, BPSK, ASK, M-ary modulation, QAM, QPSK, etc.
There is provided in accordance with the present invention a time division duplex (TDD) transceiver comprising oscillation means for generating a fundamental frequency and a plurality of harmonic frequencies, wherein the oscillation means employs a single voltage controlled oscillator (VCO), transmitter means for generating a transmit output signal in response to a Tx data input signal, the transmitter means utilizing one or more carrier signals derived from the oscillation means and receiver means for receiving and demodulating a received. signal and in response thereto, generating an Rx output signal, the receiver means utilizing one or more local oscillator signals derived from the oscillation means.
The oscillation means comprises a frequency synthesizer coupled to the output of the VCO, the frequency synthesizer having a control input and a reference input, a loop filter connected to the output of the frequency synthesizer, an adder for receiving the Tx data input and for generating a control signal input to the VCO and wherein the VCO is adapted to generate the fundamental frequency and the plurality of harmonic frequencies.
The oscillation means comprises a frequency synthesizer coupled to the output of the VCO, the frequency synthesizer having a control input and a reference input, a loop filter connected to the output of the frequency synthesizer, an adder for receiving the Tx data input and generating a control signal input to the VCO and an equalizer coupled to the output of the VCO for providing the desired frequency spectra output for the fundamental frequency and the plurality of harmonic frequencies.
The oscillation means comprises a frequency synthesizer coupled to the output of the VCO, the frequency synthesizer having a control input and a reference input, a loop filter connected to the output of the frequency synthesizer, the loop filter operative to generate a control signal input to the VCO and wherein the VCO is adapted to generate the fundamental frequency and the plurality of harmonic frequencies.
The oscillation means comprises a frequency synthesizer coupled to the output of the VCO, the frequency synthesizer having a control input and a reference input, a loop filter connected to the output of the frequency synthesizer, the loop filter operative to generate a control signal input to the VCO and an equalizer coupled to the output of the VCO for providing substantially flat frequency response output for the fundamental frequency and the plurality of harmonic frequencies.
The transmitter means is adapted to generate either an FSK signal or a BPSK signal.
There is also provided in accordance with the present invention a time division duplex (TDD) transceiver comprising oscillation means for generating a fundamental frequency, and its harmonics, wherein the oscillation means employs a single voltage controlled oscillator (VCO), transmitter means for generating a transmit output signal modulated by a Tx data input signal, the transmitter means utilizing one of the harmonic frequency components derived from the oscillation means and receiver means for receiving and demodulating a received signal so as to generate an Rx output signal, the receiver means utilizing the fundamental and the harmonics derived from the oscillation means.
The transmitter means is adapted to generate either an FSK signal, a Binary Phase Shift Keying (BPSK) signal, a Quadrature Phase Shift Keying (QPSK) signal or a Quadrature Amplitude Modulation (QAM) signal.